19 



la Valves with true raphe or pseudoraphe; ornamentation 

 transverse and/ or longitudinal 



8 



lb Valves without true raphe or pseudoraphe; ornamentation 

 radial about a central point 



2a Frustules usually united into long filaments - MELOSIRA 



Fig. 1. Melosira ambigua , (3), valves U-15u in diameter, 3-13M 

 long; wide, angular sulcus. X 1000. Abundant in the 

 Ohio and Mississippi Rivers. 



Notes : 



o 



cm 



valve view 



girdle view 



sulcus 



Fig. 2. 



Notes 



Melosira Binderana , (3), valves k- 25u in diameter, 3-7U 

 long; in valve view may be confused with Stephanodiscus 

 Hantzschii ; has distinct pores on valve mantle ( shoulder ) . 

 X 1000. Common in the Great Lakes. 



girdle view 



1. Valve length in Melosira is measured from the valve face to 

 the sulcus, along the pervalvar axis (half length). 



2. This number refers to the figure source, 



